1. Field of the Invention
The subject matter of the present invention will be discussed primarily in conjunction with use of a rotating shaft in conjunction with some form of machinery to determine speed, position and direction of movement of the shaft. However, it is considered to be within the scope of this invention that this invention could be utilized to determine speed, position and direction of movement of a lineally moving object.
2. Description of the Related Art
A rotating shaft within machinery is frequently connected with an encoder. Encoders are commonly used to sense the motion of pulleys on top of cable car towers, ski lifts, gondolas, etc. Also, encoders are used in conjunction with numerous manufacturing facilities, such as chemical plants or gasoline refineries. It is common for encoders to incorporate an electronic circuit that senses rotation of a graduated disc. The graduated disc takes the form of a rotating wheel that includes a series of evenly spaced apart openings. The electronic circuit works in conjunction with a computer to count each time the graduated disc permits light to be conducted through one of the openings and then to be blocked and then the light to be again projected through another opening, and so forth. The electronics in this manner is able to determine the position of the shaft and count the revolutions of the shaft.
These electronic devices are subject to interference to nearby electrical or electronic transmission equipment. This interference can result in the producing of an incorrect pulse which will get counted and therefor the computer will assume an erroneous position of a rotating shaft. Also, these electronics when used in harsh environments are subject to inoperability and the producing of erroneous counts. For example, encoders utilized in conjunction with ski lifts are subject to lightening strikes. Electronic encoders that are also installed in conjunction with explosive atmospheres within chemical plants or refineries are subject to causing explosions or igniting flammable materials or gases.
Prior art encoders sense angular motion by using a photodetector to detect light from a light source that typically is a light emitting diode (LED). The light from the LED is transmitted through a graduated glass disc which comprises a disc that has a mass of spaced apart openings. Each time as the disc is moved and the light is projected through an opening and then is prevented from being transmitted by the structure of a secondary static mask, a single count is produced. By counting of the sequential arrangement of the projection of the light versus the non-projection of the light, a position of a shaft can be ascertained as well as the number of revolutions that has occurred of the shaft. Encoders of the prior art are also able to determine the direction of rotation of the rotating shaft. The primary disadvantage of all prior art encoders is that such must have electronics immediately adjacent to the rotating disc and these electronics when exposed to a harsh environment subjects the encoder to inoperability or incorrect operation.
Another harsh environment for an optical encoder is when it is used in conjunction with a brake system of a vehicle wheel. Temperatures and vibrations near these wheels can be extreme and standard electronics will not provide reliability. Electrical and electromagnetic fields will also interfere with the internal electronics and/or the wiring leading to the encoder.